Grounding, Bonding, and Ground-Fault Protection
Grounding and bonding
Grounding establishes a reference to earth; bonding connects metal parts to form an effective fault-current path. Know the grounded conductor (neutral), equipment grounding conductor (EGC), grounding electrode conductor (GEC), main bonding jumper, system bonding jumper, and grounding electrode system. At a service or separately derived system, neutral and ground are bonded at one point; at subpanels they must be separated.
Sizing and protection
GEC sizing is based on the largest service or feeder conductor, while EGC sizing follows the overcurrent device rating. Ground-fault protection for people includes GFCI; for equipment, ground-fault protection of equipment may be required on large services. AFCIs address arc faults, not ground faults. Effective ground-fault current paths must be permanent, low-impedance, and capable of carrying fault current.
Traps
Do not size the EGC from the service conductor table or the GEC from the breaker rating. Watch for questions that bond neutral and ground at a subpanel, use a water pipe as the only electrode without supplemental electrodes, or assume a rod must achieve 25 ohms without the second-rod option. GFCI and AFCI are not interchangeable.
Worked example
A 200 A service with 2/0 copper service conductors: the GEC to the grounding electrode system is 4 AWG copper, but a connection to a single rod is not required to be larger than 6 AWG. The EGC for a 200 A feeder is 6 AWG copper. Rule of thumb: GEC follows service conductors; EGC follows the breaker.